The human papovavirus BKV contains a 68 base pair (bp) triplication unrelated in sequence to the 72 bp repeat of its monkey counterpart SV40. We have shown that the BKV repeats function as an enhancer by testing BKV subclones in a transient expression assay. Like SV40, the BKV enhancer activates transcription in human, monkey and mouse cells. A unique locus in the human genome has been isolated by DNA hybridization to the BKV enhancer. The homologous 1.5 kb region contains approximately 75 repeats of 21 bp with sequence similarity to the BKV repeats. In tests to assay enhancer function, the human repeats are active only in human cells, at levels 7-10X lower than the BKV repeats.